1. Field of the Invention
The present invention relates generally to a printing or copying system that includes a duplexing function, and, more particularly, to a duplexing mechanism in a substrate processing system that includes a mechanism for flexible sheet reversion.
2. Brief Description of Related Developments
In the typical copying/printing apparatus, a photoconductive insulating member is typically charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with developing powder referred to in the art as toner. Most development systems employ a developer material, which comprises both charged carrier particles and charged toner particles, which triboelectrically adhere to the carrier particles. During development the toner particles are attracted from the carrier particles by the charge pattern of the image areas in the photoconductive insulating area to form a powder image on the photoconductor area. This image may subsequently be transferred to a support surface such as copy paper to which it may be permanently affixed by heating and/or by the application of pressure, i.e. fusing. Following transfer of the toner image to a support surface, the photoconductive insulating member is cleaned of any residual toner that may remain thereon in preparation for the next imaging cycle.
Duplex copying, i.e. copying image information to both sides of a single sheet of paper, is an important feature in copying machines. Duplex copying is desirable because (i) it reduces the amount of paper required in copying in comparison to simplex (single side) copying, (ii) produces attractive copy sets, and (iii) can simulate the appearance of a printed book. Generally, such copying is accomplished in either one of two methods. In a first method, first side copies are produced in a reproduction processor and stacked in a duplex tray. When a set of first side copies is complete, the copies are fed out of the duplex tray and returned to the reproduction processor with an odd number of inversions in the total duplex path to receive second side image information, and subsequently passed to an output. Alternatively, first side copies may each be returned directly to the reproduction processor to receive second side copies thereon, without stacking, for example, as described in U.S. Pat. No. 4,660,963. This type of copying finds particular use with respect to copying two documents placed on a platen for sequential copying, sometimes referred to as two-up copying.
In conventional printing apparatus, sheet material or paper is handled by a series of rollers and counter rollers. A counter roller is required to generate forces normal to the tangential surface of a roller for handling the sheet. Counter rollers, unfortunately, lead to jams, paper tears, wrinkling, or other surface damage to the sheet. Aside from the undesired physical damage to the paper, it also requires service or maintenance and additional space is needed to allow access by service personnel to eliminate the jams.
Paper handling also typically requires a component of motion perpendicular to the direction of the roller motion. For example, in the case of paper registration, this cannot be accomplished with a standard set of rollers (a roller and counter roller). Traditional rollers form what is know in the field as a non-holonomic sheet transport system because only a few velocity directions are possible for the sheet at a given time. Instead, an additional set of rollers is required that release and grab the sheet. This adds to the cost, complexity, and the length of the paper path. Moreover, all this complexity is ultimately less reliable and at odds with the goal of reducing the space required to handle the paper.
Still another concern with paper handling in a printing apparatus is the ability to transition between different rates of speed in the paper path. As will be appreciated, in known printing apparatus, a sheet of paper undergoes numerous velocity accelerations and decelerations as it passes through the processing path. For example, a paper sheet proceeds from a stationary position at the supply, is increased in velocity to a first workstation, is decelerated at the first workstation, subsequently accelerated to a downstream or second workstation, decelerated at the second workstation, etc. Individual handling and increased processing are goals that require the paper sheets to be spaced apart as far as possible. Thus, fewer sheets can be handled in a specific time period.
On the other hand, increasing the spacing necessarily increases the velocity transitions of the paper. This, in turn, requires the rollers to continuously accelerate and decelerate to perform the velocity transitions or paper bending. The forces associated with the acceleration and deceleration place great stress on the roller and the associated motor systems. Additionally, the increased acceleration and deceleration require still further space in the assembly.
Still another concern is that when rollers in a conventional printing apparatus move paper, the paper is typically moved in primarily a forward direction, which is not always in the desired direction.
As xerographic and other copiers increase in speed, become more automatic, and do more duplicating, it is increasingly important to provide higher speed yet more economical, reliable and more automatic handling of the copy sheets being made by the copier. To be more economical it is important in a xerographic copier environment that has a duplicating function, to be able to move a paper sheet easily and not employ xe2x80x9cinversionxe2x80x9d where one roller turns a paper sheet over (i.e. exchange one face for the other) and reverses the paper sheet orientation, i.e. reverses the lead edge and trail edge orientation of the paper sheet.
With current roller technology it is difficult to revert the paper, i.e. exchange the top and bottom surfaces of the paper while maintaining the same leading edge. The primary difficulty is that with rollers, it is difficult to cause paper velocity vectors that are not parallel with the paper path. Although it is possible to construct a paper reversion system with rollers, the system would require rollers to accelerate and decelerate from process speed to zero and back for each sheet as well as posses solenoid release mechanisms. As a result of this, current duplexing machines typically invert the paper in an inverter. While this solution works, it introduces a number of added complexities and costs. First, in order to meet accuracy specifications, the paper must always be registered using the same edge. Inversion requires a duplicate set of sensors in order to accomplish trailing edge alignment. Second, because the sheets are delayed by one sheet distance in an inverter, system throughput considerations require that the paper path must be run at twice the process speed in order to maintain more than a sheet sized intercopy spacing to allow space for the returning inverted sheet. This change in velocity requires the acceleration and deceleration rollers. Third, inverters are expensive and subject to jams and wear. Hence, if paper can be reverted rather than inverted, the duplex paper-handling path can be greatly simplified.
The present invention is directed to, in a first aspect, an apparatus for processing a substrate on two sides. The substrate has a first edge as a leading edge in a process direction and a first side in a face-up orientation. In one embodiment, the apparatus comprises an input pathway for receiving the substrate from a substrate processing station, a station for processing the face-up side of the substrate, a reversion pathway for reverting the substrate and returning the reverted substrate to the input pathway. After reversion, a second side of the substrate is in the face up orientation and the first edge is the leading edge. A merge point merges the reverted substrate into the input pathway for processing the face-up side of the substrate in the print station.
In another aspect, the present invention is directed to a method of reverting a substrate in a substrate processing apparatus. In one embodiment, the method comprises transporting the substrate in a first direction along a first path. A first surface of the substrate is processed in a processing station. The substrate is decelerated along the first path and the substrate is transported in a second direction along a reversion path. The substrate is reverted in a reversion module in the reversion path. The substrate is decelerated along the reversion path and merged into the first path. The second surface of the substrate is processed in the processing station.
In yet another aspect, the present invention is directed to a mobius pathway reversion module for an electrographic system. In one embodiment, the module comprises an input pathway for receiving a substrate having a leading edge in a process direction. The module also includes a reversion pathway for reverting the substrate with the leading edge in the process direction as well as a first merge point for merging the substrate into the reversion pathway from the input pathway with the leading edge in the process direction and a second merge point for merging the substrate from the reversion pathway into the input pathway with the leading edge in the process direction.